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We are Colorado Master Gardeners volunteering at the Jefferson County CSU Extension Office. We hope you will enjoy our writings and learn something about gardening along the Front Range in Colorado. If you have questions, email us at jeffcogardener@gmail.com

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Friday, June 14, 2013

Got spider mites?
Spider mites are not insects, but are arachnids which include spiders, ticks and scorpions. They are a common pest problems on many plants, evergreens and trees in yards and gardens in Colorado. The most prevalent is the two-spotted spider mite and they are no bigger than the end of a sentence!House plants can also be host to the spider mite. One must be persistent with the pest since eliminating them can take months. Unfortunately, you may have plants or evergreens die due to a heavy infestation.

As for biological controls, various insects and predatory mites feed on this mite. One reason the spider mite becomes a problem in yards and gardens is the use of insecticides that destroys their natural enemies. Adequate watering during dry conditions can limit the importance of drought stress on spider mite outbreaks. Periodic hosing of the plant with a forceful jet of water can physically remove and kill many mites. They spread webbing under the leaves and the water may delay egg laying.

Spraying chemicals is not recommended unless the mites are numerous and natural enemies are not present. Chemical control of spider mites generally involves pesticides that are specifically developed for spider mite control. Because most miticides do not affect eggs, a repeat application at a ten to fourteen day interval is needed for control. Horticultural oils and insecticidal soaps can be utilized but oil can suffocate the plant by covering the stoma openings that the leaves use to breathe.

As for many evergreen cultivars, the soaps and oils can remove the silvery blue-gray color from the needles. The color will return in the next year's growth in most cases. Don't use sulfur spray unless it has been shown to be safe for that plant in your locality. Sulfur is a skin irritant as well as an eye and respiratory hazard, so always wear appropriate protective clothing.